UNICEF estimates there are 153 million children and adolescents in the world for whom one or both parents are deceased; millions more have been abandoned. The majority live in low- and middle-income countries such as Kenya. Compared to non-orphans, orphaned youth are at higher risk of HIV, malnutrition, other childhood morbidities, and stigma and discrimination. Our long-term goal is to gather and disseminate evidence on how to improve the health and well- being of orphans and vulnerable children so they can become healthy, well-adjusted adults. A variety of governmental and non-governmental programs and care models have emerged in an effort to fill the gap in care for the millions of orphaned children and adolescents in need. Phase I of our cohort study described models of care for orphaned and separated (abandoned) children and adolescents (OSCA) living in institutional and family-based settings and evaluated the effect of care environment on their physical and mental health. Now in its 4th round of annual assessments, Phase I suggests that OSCA in CCI's are healthier and possibly happier than those in FBS. The primary objective of Phase II is to better understand and explain these differences. We will maintain the cohort and examine specific aspects of their care environments, their cost-effectiveness, and the inter-personal characteristics that predict better physical and mental health outcomes over time and across the developmental spectrum. Enabling the present and future generations of orphaned children, adolescents and youth to develop into healthy, well-adjusted, and productive adults will yield dividends in the economic and political stability of nations such as Kenya. This work directly responds to the mission of NICHD in its aim to ensure that all children, including orphans, have the chance to achieve their full potential for healthy and productive lives, free from disease or disability, and to ensure the health, productivity, independence, and well-being of them through optimal care environments.